455-461 Series
4.5.5 Current limits (461 series)
As indicated in the "Technical characteristics" section, the 455 and 461 series contain an
internal feedback of V2.
The 461 offers two additional functions for each load current measurement:
• a linear current limit and
• a threshold current limit.
These two limits are independent.
Linear current limit
This is, in fact, a feedback of the square of the rms load
current P.
The units automatically choose the feedback which provides the best control from the two
feedbacks V2 and P.
Load with low temperature coefficient: little variation in resistance as a function of
temperature (iron alloys, nickel, chromium, aluminium, Inconel etc) feedback in V2.
For this type of load, use the "Burst firing" thyristor firing mode.
Load with high temperature coefficient: significant variation in resistance as a function of
temperature (molybdenum, molybdenum bisilicide, tungsten, platinum, etc.)
- I2 feedback at cold start
- followed by automatic change of feedback type to hot V2, enabling optimal
temperature control and feedback at all temperatures.
In this case, use the phase angle thyristor firing mode.
With the linear current limit, the "Load current / Input signal" equivalence can be adjusted
using the potentiometer marked "I limit / Limit I" on the front fascia.
Warning
This setting must always be made at maximum setpoint.
4-16
451-461 User Manual
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com